The use of polypropylene in fibers accounts for at least one-third of the end use articles derived from polypropylene world wide. Spunbond fibers are common and can be used to make fabrics useful for a variety of end uses such as medical gowns, drapes, diapers and other filtering and liquid-absorbing articles. Methods of forming polypropylenes useful in making fibers, and the properties of those fibers has been the subject of numerous patents, including U.S. Pat. No. 3,887,534; U.S. Pat. No. 4,451,589; U.S. Pat. No. 4,707,524; U.S. Pat. No. 5,726,103; and U.S. Pat. No. 6,235,664.
The wide ranging uses of spunbond polypropylene have lead to the development of spunbonding equipment capable of higher throughput. This increases the demands upon the base polypropylene, typically a controlled rheology (or “visbroken”) polypropylene. While current spunbonding equipment can produce spunbond fibers at increasing throughput, the fibers must still maintain the ability to form fabrics having the desired degree of softness and durability. Thus, polypropylene fibers of narrow denier (for softness) and high spin tension (toughness for higher throughput) are needed. What would be desirable is a spunbond fiber made from a visbroken polypropylene, and a process for forming such, that meets today's higher demands.